Heat pump (HP) systems have gained wide commercial use since their first introduction into the heating, ventilation and air conditioning (HVAC) market because of their operational efficiency and energy savings, and it is this efficiency and energy savings that appeals to consumers and is most often the deciding factor that causes them to choose HPs over conventional HVAC furnace systems. During the winter, a HP system transfers heat from the outdoor air heat exchanger to an indoor heat exchanger where the heat is used to heat the interior of the residence or building. The consumer uses a thermostat to select a temperature set-point for the interior, and the HP system then operates, using heat transferred from the outside, to warm the indoor air to achieve the set-point. As a result, the consumer enjoys a heating capability, while saving energy. Though auxiliary heating systems, such as electric or gas furnaces can be used in conjunction with the HP system, this is typically done only for a brief period of time in order to achieve the set-point in extremely cold conditions.